The present invention relates to cutting tools and, more specifically, to a cutting tool employing a plurality of indexable cutting inserts.
There are a variety of cutting tools with inserts available for performing milling operations. Indexable inserts, formed from material such as sintered carbides or ceramics, are often used in milling operations, including machining aluminum, cast iron, steel, stainless steel, nickel based alloys, cobalt alloys and titanium. One type of cutting tool uses indexable cutting inserts removably secured in insert seats spaced circumferentially around the periphery of a tool body. In these conventional cutting tools, the insert seats are oriented in the same manner with respect to the central axis of the tool body, and thus, the inserts are indexed simply by rotating them in their respective insert seats to expose a different portion of the cutting edge.
More specifically, indexable cutting inserts used in such tools are available in a variety of shapes, including round cutting inserts (also referred to as button-type inserts). Round inserts have a circular cutting edge about the periphery of the insert, which provides a number of alternately usable cutting portions. During a cutting operation, only a portion of the round cutting edge actually cuts the workpiece. When one cutting position becomes worn, the insert maybe indexed, or turned, in the seat in order to bring a fresh cutting area into the active cutting position. The number of indexable cutting positions per insert depends on the desired depth of cut. When all of the cutting positions are worn, the insert is discarded and replaced with a new one.
Some types of conventional round cutting inserts have a frusto-conical side surface, which has flat areas that provide locating and clearance areas for the insert. More specifically, for example, the frusto-conical surface has a plurality of these flat areas (also referred to as facets), that make contact with one or more side seating surfaces (also referred to as minor seating surfaces) of an insert seat for locating the insert in the seat to facilitate indexing and then to prevent the insert from rotating during operation of the cutting tool. After being located in the insert seat, the insert is secured with a screw that extends through a hole in the center of the insert and threads into a bore in the bottom seating surface (also referred to as the major seating surface) of the insert seat.
Experience reveals many considerations (some of which are competing) that need to be made in designing cutting tools with indexable inserts. These considerations, for example, include: (1) maximizing the number of inserts per tool holder; (2) preventing the inserts from rotating or slipping during cutting operation; (3) maximizing the number of indexable cutting positions per insert; and (4) providing the required depth of cut. Many of the designs used to address these considerations have shortcomings.
For example, one way to increase the number of inserts per tool holder is to reduce the amount of material at the periphery used to support the insert seat. The removal of this material was thought necessary due to machining techniques for manufacturing the tool holder. This is not desired in that it adversely affects the operating integrity of the cutting tool.
In conventional cutting inserts, the number of cutting positions per insert often corresponds to the number of facets on the insert. For example, an insert with five facets has five cutting positions. When a cutting position is worn, the insert is removed from the seat of the tool and rotated so that at least one new facet occupies the seat of the tool. The number of cutting positions per insert can be increased by adding more facets on an insert. Increasing the number of facets, however, reduces the surface area per facet which, in effect, increases the curvature of the edge surface of the insert. In turn, the reduced surface area and increased curvature hampers reliable insert location in the insert seat and increases insert slippage during machining operation.
Thus, there is a need for an improved cutting tool that increases the number of cutting positions on an insert but, at the same time, provides reliable locating of the insert in the insert seat and prevents insert rotation during cutting operations. It is preferred to increase the number of indexable cutting positions on an insert without correspondingly increasing the number of facets on the insert (or, in other words, reducing the surface area per facet). Such a cutting tool would be less expensive and more efficient than conventional cutting tools because more of the cutting edge of each insert could be used in a reliable fashion before being discarded.
In accordance with the present invention, a cutting tool is provided that overcomes the disadvantages of the prior art. The cutting tool includes a generally cylindrical cutting tool body with a central axis. The tool is adapted to be rotated in a predetermined direction about this axis. The body has a working end with an outer periphery and a plurality of seats formed in the tool body and spaced circumferentially about the outer periphery of the working end. Each of the seats has a major seating surface and at least one minor seating surface. The seats are divided into two or more sets of seats. Each set has one or more seats. The one or more minor seating surfaces of each set are angled relative to the central axis of the cutting tool body so that the angles are different between the sets.
Each set may consist of one seat. Alternatively, each set may consist of two or more seats, with the seats alternating around the circumference of the cutting tool holder between seats of different sets. There may be exactly two sets of seats and such seats alternate around the circumference of the cutting tool holder between seats of the two different sets. Each seat may be comprised of exactly two minor seating surfaces, one having a larger area than the other. In addition, the minor seating surface with the larger area may change its positions between the first and second sets of seats, from being aligned more toward the central axis to being aligned more radially along the body of the tool holder relative to the central axis. Additionally, the angle between the minor seating surfaces may be obtuse.